JP3409676B2 - Inspection method of second bonding point in wire bonding - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a second bonding point in wire bonding for connecting a chip and a substrate. 2. Description of the Related Art Wire bonding for connecting a chip and a substrate such as a lead frame or a printed circuit board on which the chip is mounted with a wire is performed as follows. First, an electrical spark is generated between the lower end of the wire drawn downward from the lower end of the capillary tool and the torch,
After the ball is mounted on the lower end of the wire, the capillary tool is lowered to bond the ball to the upper surface of the chip mounted on the substrate. Next, after the capillary tool is once moved above the substrate, the lower end of the capillary tool is lowered while drawing a predetermined locus, and the wire is bonded to the substrate (hereinafter referred to as “2nd (second) bonding”). And after wire bonding,
Resin sealing is performed to protect the chip and wires. Prior to this resin sealing, an inspection for confirming the state of wire bonding is performed to inspect whether or not normal wire bonding is performed. In the inspection performed on the second bonding point, the size and position of a so-called crescent, which is a crescent-shaped portion of the tip of the wire that is crushed in plan view by a capillary tool, are to be detected. By detecting these, it is possible to inspect whether bonding has been performed normally. Conventionally, the shape of a crescent has been detected by performing contour tracing on an image of a second bonding point. However, the shape of the crescent is likely to be lost due to various factors when being crushed by the lower end of the capillary tool, and the outline is not necessarily clear. For this reason, the method based on the contour tracking has a problem that the reliability of the inspection is low such that the contour is erroneously detected or cannot be detected in some cases. In addition, this method has a problem that it takes a long time for detection because the processing for obtaining the contour on the image sequentially is performed, and the inspection efficiency is poor. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for inspecting a second bonding point in wire bonding, which can efficiently inspect a second bonding point with high reliability. According to the second bonding point inspection method in wire bonding of the present invention, a bonding point of a pad on a substrate is imaged by a camera, and the imaging result is stored in an image storage unit as image data. A step of rotating a plurality of line segments approximating a standard crescent contour line in accordance with a wire extending angle of a bonding point to be inspected, and searching for the line segment in the bonding point image. A step of matching with a contour line, a step of obtaining an intersection of the line segment after matching and the intersection of the line segment , and specifying a crescent shape, and a step of determining a bonding state based on the approximate point Including. According to the present invention, a line segment approximating a standard crescent contour line is overlaid on the bonding point image and matched with the crescent contour line while searching.
By obtaining the intersections of these line segments and using them as approximate points for specifying the crescent shape, the second bonding point can be inspected efficiently and with high reliability. DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a second bonding point inspection apparatus in wire bonding according to an embodiment of the present invention, FIG. 2 is a plan view of a substrate on which the wire bonding is performed, and FIG. 3 is an enlarged view of the second bonding point. Side view, FIGS. 4 and 5 are enlarged image views of the second bonding point, FIG. 6 is a flowchart showing a method of inspecting the second bonding point in wire bonding, and FIGS. 7, 8, and 9 are enlarged images of the second bonding point. FIG. First, the configuration of a second bonding point inspection apparatus in wire bonding will be described with reference to FIG. In FIG. 1, a substrate 2 is placed on the stage 1. A chip 4 is mounted on the substrate 2. The pads 3 of the substrate 2 and the pads 5 of the chip 4 are bonded by wires 6. Above the stage 1 is a movable table 1 comprising an X table 9 and a Y table 10.
1 is disposed. A camera 8 is mounted on the movable table 11. The camera 8 is moved by the movable table 11 to X
The chip 4 and the substrate 2 are imaged by moving horizontally in the direction and the Y direction. An illumination unit 7 is attached below the camera 8. The illumination unit 7 illuminates the chip 4 and the substrate 2 during imaging. An A / D converter 12 is connected to the camera 8. The A / D converter 12 performs A / D conversion of the captured data into image data. The image storage unit 13 stores the A / D converted image data. The bonding coordinate storage unit 14
Bonding points, that is, pads 5 and substrate 2 of chip 4
The coordinate value of the pad 3 is stored. The processing calculation unit 15 performs a calculation necessary for determining the presence or absence of the crescent based on the image data of the bonding point. The inspection result storage unit 16 stores the determination result for each wire. The XY table control unit 17 controls the operation of the movable table 11. The standard pattern storage unit 18 stores graphic data that approximates the standard crescent shape. The circuit pattern storage unit 19 stores a rotation pattern obtained by rotating the figure in accordance with the extension angle of each wire. The threshold value storage unit 20 stores a threshold value of a matching ratio for determining the presence or absence of a crescent. Program storage unit 21
Stores a sequence program that causes each unit to perform an inspection operation. The display unit 22 displays an image captured by the camera 8. Next, wire bonding points to be inspected will be described with reference to FIG. In FIG. 2, a chip 4 is mounted on the substrate 2. A large number of pads 5 are formed on the upper surface of the chip 4 along the edge. On the substrate 2, pads 3 are formed at positions corresponding to the respective pads 5 of the chip 4. The pads 5 of the chip 4 and the pads 3 of the substrate 2 are connected by wires 6.
The bonding point of the pad 5 is the first bonding point, and the bonding point of the pad 3 of the substrate 2 is the second bonding point 30. The extending angle α of the wire 6 extending from the pad 5 varies depending on the bonding point 30. Next, the second bonding point 30 will be described with reference to FIG. A wire 6 is bonded to the upper surface of the pad 3 of the substrate 2. 31a, 31b, 3
1c shows the movement of the lower end portion of the capillary tool for bonding the wire 6 in the order of operation. First, 31a indicates a position at the timing when the lower end portion of the capillary tool starts to press the wire 6 against the pad 3. Thereafter, the capillary tool further descends while pressing the wire 6 against the pad 3 and moves laterally toward the bonding point.
At the position 1c, the upper surface of the pad 3 is pressed downward to form a concave-shaped indent 32. At this time, in the process in which the capillary tool moves from 31a to 31b, the wire 6 is crushed by the lower end of the capillary tool to form the sloped portion 6b. The second bonding point inspection apparatus in the wire bonding is constructed as described above, and the second bonding point inspection method will be described below. First, as shown in FIG. 1, the substrate 2 on which the chip 4 is mounted is placed on the stage 1. Next, movable table 1
1 is driven to move the camera 8 above the second bonding point 30 to be inspected, the illumination unit 7 is turned on, and the second bonding point 30 is imaged by the camera 8.
The imaged data is sent to the image storage unit 13 via the A / D conversion unit 12 and stored as image data. This image data is read into the processing calculation unit 15, and the image data is subjected to image processing calculation for inspection. Here, an image obtained by imaging with the camera 8 will be described. In FIG. 3, the downward arrow e indicates the incident direction of the illumination light, and the upward arrow f indicates the reflection direction of the reflected light. The light incident on the upper surface of the pad 3 is reflected upward, and the light incident on the wire 6 and the sloped portion 6b of the wire 6 is reflected in an oblique direction. The wire 6 and the sloped portion 6b have different brightness. Therefore, by performing binarization processing or multi-value processing on the image data, the upper surface of the pad 3 is made a bright image as shown in FIG. 4 and the wire 6 and the sloped portion 6b shown in FIG. Thus, an image having a dark image of the so-called crescent 6c can be obtained. A method for inspecting the bonding state based on the image thus obtained will be described. First, a standard pattern representing the shape of the crescent 6c will be described with reference to FIG. As a standard pattern, FIG.
As shown in (a), an arc a as a line segment approximating the contour line A of the crescent 6c, an arc b as a line segment approximating the contour line B, and the starting point of the crescent 6c (the tip of the expansion of the crescent 6c) ) A start point standard pattern c representing a standard shape around Pi and an end point standard pattern d representing a standard shape around the end point of crescent 6c (boundary portion of crescent 6c and wire 6) Pt are set. . These standard patterns are set according to the accuracy level required for the inspection based on experience data. That is, in this embodiment, an arc is used as a line segment that approximates the contour line, but inspection accuracy can be improved by using something other than an arc, for example, an ellipse or a parabola that can approximate the shape of the crescent 6c with better accuracy. Can be further enhanced. In addition, when performing a very rough inspection, the simplest straight line can be selected as an approximate line segment. By matching these standard patterns with the image of the crescent portion on the image of the second bonding point, the contour line A of the crescent 6c is not required without processing that requires processing time such as contour tracking on the image.
B can be obtained approximately. Further, the standard patterns c and d of the starting point and the end point are searched around the intersection point of the above-obtained outlines A and B, and matching is performed, so that the starting point Pi and the end point Pt of the crescent 6c are obtained in the actual state. It can be estimated according to the tendency of the crescent shape. These standard patterns are stored in the standard pattern storage unit 18. As shown in FIG.
By rotating the image of each standard pattern on the screen according to the wire extension angle α and crescent spread angle β of the bonding point to be inspected, an image that almost matches the actual inclination of the bonding point image Can be obtained. That is, by rotating the arc a by the wire extension angle α, the arc a ′ matching the inclination of the contour A is obtained.
When the arc b is rotated by the wire extension angle α and returned by the crescent spread angle β, an image of the arc b ′ that matches the inclination of the contour line B is obtained. The arc b ″ is a symmetrical figure with respect to the wire extension line of the arc b ′. Similarly, by performing a necessary rotation operation on the image of the start point standard pattern c and the end point standard pattern d, images c ′, c ″, d ′, d ″ corresponding to the respective parts shown in FIG. 5 are obtained. be able to. The second bonding point inspection method will be described below with reference to the flowchart of FIG. First, as shown in FIG. 5, a rotation pattern in which the arc a is rotated according to the extension angle α of the wire 6 is created, and the rotation pattern storage unit 19
(ST1). Subsequently, the arc b is similarly rotated according to the extending angle α of the wire 6 and the spreading angle β of the crescent 6c (ST2). By these operations, the directions of the circular arcs a ′ and b ′ after the rotation substantially coincide with the directions of the contour lines A and B of the crescent 6c. Next, as shown in FIG. 7, arcs a 'and b'.
Are searched in the X and Y directions within a preset range, and the positions that best match the contour lines A and B are obtained (ST3). This matching process does not have to be performed in the entire range of each of the contour lines A and B, but it is only necessary to identify a range in which the contour characteristics of the contour lines A and B appear the most and perform matching only in this specific range. By specifying the processing target range in this way, it is possible to shorten the processing time and perform the inspection more efficiently. These arcs a ', b', b ''
If the position that best matches the contour lines A and B is specified, these arcs a ′, b ′,
Find intersection points P1, P2, and P3 of b ″, and Crescent 6c
These points are approximate points that specify the position and shape (ST4). Thereafter, the start point standard pattern c and the end point standard pattern d stored in the standard pattern storage unit 18 are read out, and after performing a predetermined rotation operation, the corresponding approximate points P1, P
2, matching is performed around P3 (ST5). Thereby, the positions of the start point Pi and the end point Pt on the start point standard pattern c and the end point standard pattern d can be made to correspond to the coordinates on the image of the actual bonding point, and the crescent 6
The start point Pi and the end point Pt of c can be estimated with high accuracy. In this matching process, if the image around the approximate point is unclear, a good matching result cannot be obtained, and if the starting point Pi of the crescent 6c cannot be obtained clearly (ST6), it is obtained in ST4. Approximate point P1,
P2 is adopted as the crescent start point (ST7). Next, if the end point Pt of the crescent 6c cannot be determined clearly for the same reason (ST8), processing for determining the end point Pt is performed using the end point subpattern described below (ST).
9). As shown in FIG. 9, this processing uses the pattern of the bright image portion 6d appearing in the image of the wire 6 where the wire 6 is transferred to the crescent 6c, and the crescent end point P is obtained.
t is estimated. In this portion, the wire 6 is bent (see FIG. 3). The reflected light in this portion enters the upper camera 8 and the bright image portion 6d having a high brightness appears in a pattern having a certain tendency. Since the pattern of the bright image portion 6d and the position of the end point Pt of the crescent 6c are correlated, the end point P is determined by specifying the position of the bright image portion 6d.
t can be estimated. That is, by standardizing this pattern and setting an end point sub-pattern that identifies the positional relationship with the end point Pt, and matching this end point sub-pattern over the bonding point image,
The position of the end point Pt can be estimated. If the end point Pi is still not clearly obtained even as a result of the processing by the end point sub-pattern (ST10), the approximate point P3 is adopted as the end point (ST11). Thereafter, the center of the crescent 6c is calculated based on the start point Pi and end point Pt obtained in the above flow (ST12), and output as a crescent position. Based on the crescent position, the bonding state is determined (ST13). In this way, a standard pattern of each characteristic portion representing the shape of the crescent 6c is set in advance according to the required inspection accuracy, and this standard pattern is overlapped with the captured image and matched to obtain the required inspection. By obtaining the result by estimation, the inspection processing time can be greatly shortened and the inspection efficiency can be improved. Further, even when an unclear part or noise is present in the crescent contour on the image, the uncertain part is supplemented by the standard pattern, so that the inspection result can be obtained reliably within the required accuracy range. According to the present invention, line segments that approximate standard crescent contour lines are matched with the crescent contour lines while searching by superimposing the line segments on the bonding point image. As the approximate points to identify the crescent shape by finding the intersection of the two, the bonding state of the second bonding point is inspected based on these approximate points, greatly increasing the processing time required for inspection on the image Therefore, the inspection of the second bonding point can be efficiently performed at a high speed, and a highly reliable inspection result can be obtained even when there is noise or an unclear part on the image.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the configuration of a second bonding point inspection apparatus in wire bonding according to an embodiment of the present invention. FIG. 3 is an enlarged side view of a second bonding point according to an embodiment of the present invention. FIG. 4 is an enlarged image view of a second bonding point according to an embodiment of the present invention. Fig. 6 is an enlarged image view of a second bonding point according to an embodiment. Fig. 6 is a flowchart showing a method for inspecting a second bonding point in wire bonding according to an embodiment of the invention. Fig. 7 is a flowchart showing a second bonding point according to an embodiment of the invention. Fig. 8 is an enlarged image of a point. Fig. 8 is an enlarged image of a second bonding point according to an embodiment of the present invention. Fig. 9 is a second image of an embodiment of the present invention. Enlarged image of bonding point [Explanation of symbols] 2 Substrate 3 Pad 4 Chip 5 Pad 6 Wire 6c Crescent 8 Camera 11 Movable table 13 Image storage unit 15 Processing operation unit 18 Standard pattern storage unit 20 Threshold storage unit

──────────────────────────────────────────────────── ─── Continued from front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01B 11/00-11/30 G01N 21/84-21/958 G06T 1/00-9/40 H01L 21 / 60 H01L 21/66

Claims (1)

(57) [Claims] [Claim 1] Approximating a standard crescent contour with a step of imaging bonding points of a pad on a substrate by a camera and storing the imaging result as image data in an image storage unit Rotating a plurality of line segments according to the wire extension angle of the bonding point to be inspected, matching the crescent contour line while searching for the line segment in the bonding point image, and after matching Before the line segment
A method for inspecting a second bonding point in wire bonding, comprising: a step of obtaining an intersection point of a line segment and using a rough point for specifying a crescent shape; and a step of determining a bonding state based on the rough point.